1. Field of Invention
The present invention relates to a package substrate, and more particularly, to a package substrate in which the structural strength of a thin circuit board is reinforced.
2. Description of Related Art
In recent years, as the rapid progress of the electronic technology, high-tech electronic products have been developed, thus human-oriented electronic products with preferred performance have brought forth a new era, and have been designed to cater to the trend of being light, thin, short, and small.
Referring to FIG. 1, FIG. 1 is a schematic view of a conventional package substrate. To enhance the strength of a package substrate 100, a copper foil substrate 120 with a core layer 110 containing glass fiber and epoxy resin is used to fabricate the inner circuit of the package substrate 100. The thickness of the copper foil substrate falls within a range of 400-800 μm, and desirable circuit layers 122, 124 are formed on two opposite surfaces of the copper foil substrate through a patterned etching process. However, although the copper foil substrate 120 with a greater thickness is useful for enhancing the strength and supportability of the package substrate 100, the electrical transmission speed of the circuit layers 122 and 124 is reduced accordingly. Therefore, in order to meet the requirements of a thin substrate, the thickness of the core layer 110 in the conventional package substrate 100 has to be reduced, so as to accelerate the transmission of electronic signals.
However, as the thickness of the thin substrate is reduced, it cannot provide adequate supportability to meet the flatness requirements. Particularly, during the bumping process in a high-temperature environment, as the thin substrate is heated, the warpage of the thin substrate becomes even serious, which cannot meet the requirements of the manufacturing process.